Let's take a look at the science of conceiving a baby girl. When trying to conceive a baby girl, it is first important to understand how conception works. The Y-carrying sperm (the one that results in a baby boy) is smaller and faster than the X-carrying sperm (the one that allows you to conceive a baby girl). The X (female) chromosome is slower, but more resilient. It moves through the acidic environment more slowly and safely to fertilize the egg in order to conceive a baby girl.
If you want to conceive a baby girl, your chances are higher when you have intercourse two to three days prior to ovulation, as the male sperm is faster and will arrive first, find that there is no egg and die off. In order to have the best chance of conceiving a baby girl, you need to pinpoint when it is that you are fertile. There are multiple ways to do this, and the more things you do, the better your chances.
PLEASE KEEP IN MIND - even if you did every single one of these, it's still not a 100% guarantee... but it helps your chances significantly. The natural rate to conceive a girl is 55%. If you follow the diet, and watch your ovulation time religiously, you can up that chance to 80-85%.
A fertility tracker system uses your saliva to help determine your daily fertile status. Levels of estrogen in your saliva indicate when pre-ovulation begins, and as estrogen rises, a woman will be able to view a full pattern of ferns with a peak just a day or so prior to ovulation.As light ferning can begin to occur three days prior to ovulation, this is the best time to conceive a baby girl. With 100 times magnification (twice as strong as other lipstick model fertility monitors), the Fertility Tracker allows you to spot your fertile days and predict ovulation long before other models.
You can chart your temperature and track your cervical mucous as well, also known as "Natural Family Planning.
Two methods of natural family planning are currently taught. The first is the mucus or ovulation method. In this method, the days just before and just after ovulation are determined by checking the woman's cervical mucus. When a woman is most likely to become pregnant, the cervical mucus is stretchy, clear and slick. The mucus during this time looks and feels much like an uncooked egg white. Shortly before reaching the "eggwhite" stage, most women will notice their they are "wetter", but it will not be stretchy discharge.
The second method is called the symptothermal method. With this method, the woman takes her temperature each day with a basal body temperature thermometer and writes it down on a chart. At the time of ovulation, a woman's temperature will rise slightly (about .9°F). The woman also checks the consistency of her cervical mucus like she does with the mucus method. She may also notice other changes, such as pain in the area of the ovaries, bloating, low backache and breast tenderness.
Another step is to watch your diet. For a girl, try a pre-conception diet rich in calcium and magnesium. Cut down intake of salty foods and red meat. This will make your vagina more friendly to the X sperm, and LESS friendly to the Y sperm. This means, no chips and steak. Yogurt and fish are great.
Sex position also is posed to have an effect. As the Y sperm are faster, but less resilient, especially if you've been following the diet, this can make a difference. For girl conception, try to have more shallow penetration. You want the male sperm to die before they reach the egg, and the females to get through, so the further from the cervix the ejaculation occurs, the more the males have to get through to get to the egg.
I'm trying to keep this purely scientific. Everything here is based off of scientific fact. There are other suggestions, such as the Chinese Lunar Calendar, but if you're seriously trying for a girl, go for science.